Yes, actually this has always been the issue with FIFA, it is not a placebo effect. Even from the PS2 era, I remember PES 5, 6 always having larger pitch size compared to FIFA 06, 07. The same is the case for the PS3, PS4 versions and of-course the PC ports.

EA have never addressed the sizes of their football pitch. What they have done in essence is redesign new stadiums and graphics under the same size template which they reused all these years.

It has been asked many times, but it seems like a tough ask because EA need to rebuild a whole pitch from scratch! I'm not sure if it is possible to resize the existing pitch. But even then, it needs some work so that you can design proper size goal nets, corner flags, stadium size, etc to be in complete harmony with the enlargement of the pitch.

I guess you're right. Perhaps the gameplay speed also contributes to that illusion of a larger pitch. In PES gameplay speed has always traditionally been slower than FIFA.

Slower gameplay speed means it takes longer for players to travel from one pitch to the other. FIFA gameplay being faster means the players reach one side of the pitch to the other in no time making it look smaller.

Although I still do feel the PES pitch is a little bit longer, but the slower speed also contributes to that placebo effect.